Group of Tobias Hurth

Particle Physics Phenomenology within and beyond Standard Model:

  • Interplay of Collider and Flavour Physics in the New Physics Search
  • Perturbative and Nonperturbative Corrections to FCNC Processes
  • Standard Model Effective Field Theory (SMEFT)
  • Soft Collinear Effective Theory (SCET) and other Field Theoretical Methods
  • QCD Corrections
  • CP Violation

The main concern of elementary particle physics is to understand the basic dynamical structure of matter. The Standard Model (SM) of elementary particles, a local gauge theory, describes almost all phenomena of the strong, weak, and electromagnetic interactions between the fermionic matter in a unified way, emphasizing the local gauge principle as the basic dynamical concept. And recently, the Higgs mechanism has been shown to be responsible for the masses of the fundamental particles.

Flavour physics deals with that part of the SM which differentiates between the three families of fundamental fermions. These are the left-handed doublets containing quarks and leptons and the corresponding right-handed singlets.

By now all measurements of flavour-violating processes between quarks are governed by a 3×3 unitarity matrix, the Cabibbo-Kobayashi-Maskawa (CKM) matrix of the SM. The CKM matrix is fully described by four real parameters, three rotation angles and one phase. It is this phase that represents the only source of CP violation in the SM and that allows for an unified description of all the CP violating phenomena. This is an impressing success of the SM and the CKM theory.

Open problems like the hierarchy problem, dark matter, and the matter-anti-matter asymmetry suggests the existence of new degrees of freedom beyond the SM. Flavour physics plays an important role in the search for them.

In principle, there are two ways to search for possible new degrees of freedom. At the high-energy frontier we try to produce those new degrees of freedom directly, while at the high-precision frontier we analyze the indirect virtual effects of such new particles within flavour or electroweak observables. Flavour changing neutral currents (FCNCs) test the SM directly on the one-loop level offering high sensitivity to potential new degrees of freedom beyond the SM. Thus, FCNC decays and CP violating observables give complementary information about the SM and its extensions.

In view of the present status in particle physics our research focus on the following topics:

  • Theoretical predictions of specifically suitable observables in flavour physics are calculated to high precision in order to explore possible degrees of freedom beyond the SM. For example in the inclusive so-called penguin modes b>sgamma and b>sll subleading corrections become important like non-perturbative contributions.

  • The phenomenological implications of models beyond the SM and correlations of collider and flavour physics are analysed. Moreover, flavour and electroweak precision data are combined.  Standard Model Effective Theory is the appropriate tool to work out such correlations.

  • Effective field theoretical methods like soft-collinear effective theory (SCET) are further developed in order to reach a deeper understanding of the non-perturbative contributions in exclusive B decays which is crucial for the new physics sensitivities of the present LHCb and BELLE-II experiments.

  • Open questions in neutrino physics, regarding their masses, their mixing and their particle nature, are actively being addressed in the present and future experimental program. Correlations of neutrino properties with flavour phenomena in the charged-lepton and in the quark sector are analysed.

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